The present invention relates to a motorcycle mounted with an engine in which a breather chamber is disposed on an upper surface portion of a crankcase of an engine.
Many of straddle type motorcycles have such a structure that a fuel tank is installed on a front half upper portion of a motorcycle frame, a seat is provided at the rear portion thereof, and the engine is mounted below the fuel tank.
In a case where the engine is an in-line multi-cylinder type, as disclosed in Japanese Patent Laid-open Publication No. HEI 8-86223, the motorcycle often has a layout in which a cylinder block and a cylinder head are mounted on a front portion of an upper surface of a crankcase of the engine, and a crankshaft and a transmission shaft extending in the frame width direction are pivotally supported inside of the crankcase.
The engine disclosed in this publication has a structure that a cylinder block and a cylinder head are provided in a forward inclined manner on the front portion of the upper surface of the crankcase which is vertically splitable into three sections, comprising an upper case section, a middle case section and a lower case section, a crankshaft is pivotally supported on a mating surface portion (joint portion) between the upper case section and the middle case section, and two transmission shafts are pivotally supported on a mating surface (joint portion)between the middle case section and the lower case section. In this manner, the crankshaft and the transmission shafts are pivotally supported in a stepped arrangement from each other, and a distance between axes of the crankshaft and the front transmission shaft is reduced, thus making small a size of the crankcase (i.e. engine) in the front and rear direction (longitudinal direction of the motorcycle body).
With such an in-line multi-cylinder structure engine, a breather chamber is integrally provided on the rear portion of the upper surface of the upper case section of the crankcase. The breather chamber acts as an oil separation chamber having a labyrinth structure with a predetermined capacity and is adapted to alleviate a pressure change in the crankcase occurring with a reciprocal motion of a piston of a piston-cylinder assembly of the engine and leakage of a blowby gas without jetting externally the oil stored in the crankcase outside. As the capacity of the breather chamber increases, vapor-liquid separability of the blowby gas and the oil becomes better, thus making the operation of the engine smooth.
However, main components of the engine, such as crankcase, cylinder block and cylinder head, are generally formed of aluminum castings, and the outer wall of the breather chamber integrally provided on the upper case section of the crankcase is also formed of an aluminum casting. Therefore, as the capacity of the breather chamber increases, the weight of the engine also increases, and as a result, it becomes hence difficult to make increase the capacity of the breather chamber.
Moreover, even if there is adopted a structure in which the capacity of the breather chamber is increased, no enough space will exist in the vicinity of the crankcase, because supplementary equipments or members such as starter motor and water pump are installed in the vicinity of the crankcase. Thus, it is considered as only one option to increase the height dimension of the breather chamber. However, if the height of the breather chamber is made high over the mating surface portion between the upper case section of the crankcase and the cylinder block of the engine, it becomes difficult to work or assemble the uppercase section of the crankcase, which will involve an increase of the production cost of the engine.
An object of the present invention is to substantially eliminate inconveniences or difficulties encountered in the prior art mentioned above and to provide a motorcycle capable of reducing a production cost of the engine and improving a layout of supplementary machinery around the engine, while improving the breather performance and light weight of the engine.
This and other objects can be achieved according to the present invention by providing, in one aspect, a motorcycle in which an engine is mounted below a fuel tank and an air cleaner, the engine includes a cylinder block and a cylinder head inclined forward on an upper front portion of a crankcase of the engine in an engine installed state, the crankcase comprising a plurality of vertical case sections including an upper case section, a middleclass section and a lower case section, the crankshaft is pivotally supported at a mating portion between the uppercase section and the middle case section and a transmission shaft is pivotally supported on a mating portion between the middle case section and the lower case section,
wherein the upper case section is integrally formed with a lower portion of the cylinder block, and a breather cover manufactured independently is provided in a forward inclined manner so as to cover an upper surface of the middle case section at the rear portion of the uppercase so as to define an interior of the breather cover as a breather chamber and a breather hose extends substantially perpendicularly upwards from a rear upper portion of the breather cover and is connected to the air cleaner at a bottom portion thereof.
In preferred examples of the above aspect, the breather cover is provided substantially at an intermediate position in a width direction of a motorcycle frame extending in the longitudinal direction of the motorcycle body, a starter motor for the engine is mounted on one side of the breather cover and a water hose for a liquid-cooled-engine extending from a water pump is arranged on the other side thereof.
A breather hose extending from the rear upper portion of the breather cover extends between a fuel pump disposed to protrude downward from a rear lower surface of the fuel tank and a fuel feed pipe of a fuel supply system located in front of the fuel pump and is connected to the air cleaner.
A portion in a mating portion between the middle case section and the breather cover is recessed downward so as to form a breather recess with a bottom surface inclined forward, a breather hole is formed in the vicinity of an intermediate portion in the front and rear direction of a side wall of the breather recess so as to form an oil return path in the vicinity of the front end on the bottom surface, so that the breather hole and the oil return path are respectively communicated with an interior of the crankcase, a gasket is interposed between the breather recess and the breather cover, the interior of the breather cover is divided by partition walls so as to form a plurality of compartments which lie in a row along the front and rear direction of the engine and communicate with each other, an opening is formed to the gasket so that the front most compartment is communicated with the front end portion of the breather recess, and an extension of the breather hose is communicated with the rearmost compartment.
The mating portion between the middle case section and the breather cover is formed in parallel with the mating portion between the middle case section and the upper case section so as to provide same height level.
In a modified aspect, there is provided a motorcycle comprising:
a motorcycle body provided with a body frame extending in a longitudinal direction thereof;
a steering member supporting a front wheel to be rotatable and connected to the body frame;
a swing arm unit mounted to the body frame and connected to a rear wheel to be rotatable;
an engine disposed substantially central portion of the motorcycle body and including a crankcase, a cylinder block and a cylinder head in a forward inclined manner in a standing state of the motorcycle, the crankcase being separated into a plurality of vertical case sections comprising an upper case section, a middle case section and a lower case section so that a crankshaft is pivotally supported to a mating portion between the upper and middle case sections;
a transmission shaft pivotally supported to a mating portion between the middle and lower case sections;
a fuel tank disposed above the engine;
a seat member disposed to a rear portion of the fuel tank;
a fuel supply unit disposed at a rear upper portion of the engine; and
an air cleaner disposed above the fuel supply unit,
wherein the upper case section is secured to a lower portion of the cylinder block, and a breather cover is provided in a forward inclined manner so as to cover an upper surface of the middle case section at the rear portion of the upper case so as to define a breather chamber in the breather cover and a breather hose extends upward from a rear upper portion of the breather cover and is connected to the air cleaner at a bottom portion thereof.
According to the structures and subject features of the present invention mentioned above, since the breather cover is provided independently from the uppercase section, the breather cover can be formed of a material lighter than that of the upper case section formed of an aluminum casting. Moreover, since the height dimension of the breather cover can be increased, regardless of the shape of the upper case, the capacity of the breather can be increased.
The improvement in the breather performance and light weight of the engine can be both contemplated. The breather chamber having a large capacity can be provided without impairing the layout of the supplementary machinery around the engine.
Moreover, according to the preferred examples of the present invention, since the breather hose is arranged substantially in the perpendicular direction, vapor-liquid separability of the blowby gas and the oil becomes excellent to thereby improve the breather performance.
Furthermore, the interior of a large-capacity breather chamber composed of the breather cover and the breather recess is divided by the gasket and the partition walls and formed like a labyrinth. Moreover, the extension of the breather hose and the oil return path are located on the uppermost portion and the lowermost portion of the breather chamber, respectively. Accordingly, the vapor-liquid separability of the blowby gas and the oil can be improved in the crankcase, thereby improving the breather performance.
Furthermore, the mating portion with the uppercase section and the mating portion with the breather cover in the middle case section of the crankcase can be made flat at the same time, and hence, the middle case section can be easily manufactured, thus reducing the production cost of the engine.